JP6910257B2 - Beelight manufacturing method - Google Patents

Description

The present invention is capable of obtaining a belite (C 2 _S) having excellent strength development, a method for producing a belite.

Traditionally, in the cement industry, as one of the efforts to save energy and build a low-carbon society, a low-calcium hydraulic composition that reduces the amount of limestone, which is the main raw material of Portland cement, has been developed. ing. _{As such a low-calcium hydraulic composition, specifically, the content of belite (C 2} S) is reduced while reducing the content of _{alite (C 3} S), which is a main mineral of cement clinker, in Portland cement. Examples thereof include hydraulic compositions having an enhanced mineral composition.

As described above, when the alite content is reduced in Portland cement, a decrease in strength characteristics, particularly a decrease in initial strength development up to 28 days of age, becomes a problem in terms of quality. Therefore, belite, which is positioned as a substitute for alite in terms of mineral composition, is required to have more excellent strength expression, and various attempts have been made.

For example, in Patent Document 1, fine-grained calcium silicate hydrate obtained by hydrating a CS-based cement clinker mineral in a wet mill is filtered and dried, and then calcined at 600 to 1000 ° C. , A method for obtaining highly active belite is disclosed.

Japanese Unexamined Patent Publication No. 6-247754

However, the method of Patent Document 1 has been confirmed by the present inventors to have low reproducibility, and there is still room for improvement as a method for surely obtaining belite having excellent strength development.

Therefore, an object of the present invention is to provide a production method for reliably and easily obtaining belite having excellent strength development.

Therefore, as a result of various studies, the present inventors have found that a specific method using two kinds of aqueous solutions can surely obtain belite having excellent strength development, and have completed the present invention. rice field.

That is, in the present invention, the following steps (X) and (Y):
(X) A step of mixing an aqueous solution of a silicic acid compound and an aqueous solution of a calcium compound to obtain a precursor (A), and (Y) the obtained precursor (A) is calcined at a temperature of 800 ° C. or lower to beerite. It provides a method for producing belite, which comprises a step of obtaining the above.

According to the production method of the present invention, it is possible to realize a production method by a so-called coprecipitation method using two kinds of aqueous solutions, and it is possible to reliably and easily obtain belite having excellent strength development.

Hereinafter, the present invention will be described in detail.
The method for producing belite of the present invention comprises the following steps (X) and (Y):
(X) A step of mixing an aqueous solution of a silicic acid compound and an aqueous solution of a calcium compound to obtain a precursor (A), and (Y) the obtained precursor (A) is calcined at a temperature of 800 ° C. or lower to beerite. It is provided with a process of obtaining. The production method of the present invention is a method for producing belite by the coprecipitation method using two kinds of aqueous solutions as described above.

The step (X) provided in the method for producing belite of the present invention is a step of mixing an aqueous solution of a silicic acid compound and an aqueous solution of a calcium compound to obtain a precursor (A). That is, it is a step of obtaining a precursor (A) by using an aqueous solution a obtained by mixing an aqueous solution of a silicic acid compound and an aqueous solution of a calcium compound.

The aqueous solution of the silicic acid compound used in the step (X) is not particularly limited as long as the silicic acid compound is dissolved in water or water and an acid. As such a silicic acid compound, sodium silicate (Na ₂ O, nSiO ₂ , mH ₂ O) is preferable from the viewpoint of easy availability and excellent handling. When sodium silicate is used as the silicic acid compound, the _{coefficient n indicating the SiO 2} / Na ₂ O molar ratio is 0.5 in _{the chemical composition formula (Na 2} O · nSiO ₂ · mH ₂ O). It is more preferable to use sodium silicate.

The Si concentration of the aqueous silicic acid compound is preferably 0.3 to 1.0 mol / L by appropriately adjusting the amount of water.

Further, the pH of the silicic acid compound aqueous solution at 25 ° C. is from the viewpoint of suppressing excessive fluctuation of the Si chain length of the precursor (A) depending on the pH of the aqueous solution a obtained by mixing with the calcium compound aqueous solution. It is preferably 10 to 14, and more preferably 12 to 13. A general-purpose pH adjuster such as nitric acid or caustic soda can be used to adjust the pH of the aqueous solution of the silicic acid compound.

The calcium compound aqueous solution used in the step (X) is not particularly limited as long as it is dissolved in water or water and an acid, and specific examples thereof include a calcium sulfate aqueous solution, a calcium nitrate aqueous solution, and a calcium acetate aqueous solution. ..

The Ca concentration of the aqueous calcium compound solution is preferably 0.6 to 5.0 mol / L by appropriately adjusting the amount of water.

Further, the pH of the calcium compound aqueous solution at 25 ° C. is from the viewpoint of suppressing excessive fluctuation of the Si chain length of the precursor (A) depending on the pH of the aqueous solution a obtained by mixing with the silicic acid compound aqueous solution. It is preferably 2 to 13, and more preferably 4 to 12. A general-purpose pH adjuster such as nitric acid or caustic soda can be used to adjust the pH of the calcium compound aqueous solution.

The silicic acid compound aqueous solution and the calcium compound aqueous solution are preferably mixed in the obtained aqueous solution a so that the Ca / Si molar ratio is 1.9 to 2.1.
When mixing the silicate compound aqueous solution and the calcium compound aqueous solution, it is preferable to add the calcium compound aqueous solution to the silicate compound aqueous solution and mix them. Before adding the calcium compound aqueous solution, the silicate compound aqueous solution is stirred in advance. It is more preferable to keep it. The stirring time of the aqueous solution of the silicic acid compound is preferably 1 to 120 minutes, more preferably 1 to 60 minutes.

The pH of the obtained aqueous solution a is preferably 9 to 14, and more preferably 10 to 13.

Further, it is preferable that the aqueous solution a is continuously stirred even after the silicic acid compound aqueous solution and the calcium compound aqueous solution are mixed. By continuing stirring, the reaction rate is increased, and the precursor (A) can be effectively produced in the aqueous solution a. The stirring time of the aqueous solution a is preferably 0.5 to 48 hours, more preferably 12 to 36 hours immediately after the silicic acid compound aqueous solution and the calcium compound aqueous solution are mixed.

In addition, when stirring the aqueous solution a, it is preferable to heat the aqueous solution a, specifically, it is preferably heated to 20 to 90 ° C. and stirred, and it is heated to 30 to 70 ° C. and stirred. Is more preferable.

Further, from the viewpoint of preventing carbonation of calcium in the aqueous solution a, it is preferable to purge nitrogen into the calcium compound aqueous solution before mixing with the silicic acid compound aqueous solution and the obtained aqueous solution a, and stirring the aqueous solution a. When continuing, it is preferable to carry out such stirring in an atmosphere of an inert gas such as nitrogen.

The precursor (A) can be recovered by filtering the aqueous solution a. Examples of the filtration means include vacuum filtration, pressure filtration, centrifugal filtration and the like, but pressure filtration such as a filter press is preferable from the viewpoint of ease of operation and the like.

The precursor (A) recovered by filtration is preferably washed with water from the viewpoint of removing impurities, for example, sodium salts when sodium silicate is used in the aqueous solution of the silicic acid compound. The amount of washing water used for washing is preferably 2 parts by mass or more, and more preferably 5 parts by mass or more, based on 1 part by mass of the precursor (A) in the filtration residue.

After washing, the precursor (A) is preferably filtered and recovered as a cake having a water content of 10 to 50% by mass. As the means of filtration, the same as the above-mentioned filtration, vacuum filtration, pressure filtration, centrifugal filtration and the like can be mentioned, but from the viewpoint of ease of operation and the like, pressure filtration such as a filter press is preferable. If the precursor (A) after filtration is not promptly moved to the next step (Y), it is preferably a dried product from the viewpoint of suppressing carbonation of the precursor (A) in the dehydrated cake. The drying temperature is 80 to 120 ° C., more preferably 100 to 120 ° C., and the drying time may be constant at such a drying temperature, and the drying time is 30 to 120 minutes, more preferably 60 to 120 minutes.

The precursor (A) obtained through the step (X) is a mixture containing calcium silicate hydrate (hereinafter referred to as "CSH") and calcium hydroxide as the main phase. The Ca / Si molar ratio of the precursor (A) is preferably 1.9 to 2.1.

The ignition loss (950 ° C. constant weight) of the precursor (A) is a value relating to the precursor (A) dried to a constant weight at a temperature of 110 ° C., preferably 11% by mass or less, and more preferably 9% by mass. It is as follows. When the ignition loss of the precursor (A) exceeds 11% by mass, the content of the contaminating phase other than CSH or calcium hydroxide in the precursor (A) becomes excessive, and the obtained belite May affect the strength development of calcium hydroxide.

The step (Y) provided in the method for producing belite of the present invention is a step of calcining the precursor (A) obtained in the step (X) at a temperature of 800 ° C. or lower to obtain belite.

The firing temperature in the step (Y) is 800 ° C. or lower, preferably 400 to 800 ° C., and more preferably 500 to 700 ° C. from the viewpoint of effectively increasing the specific surface area of the obtained belite. The baking time is preferably 1 to 6 hours, more preferably 1 to 4 hours when the precursor (A) is a dehydrated cake, and preferably 30 minutes to 30 minutes when the precursor (A) is a dried product. 5 hours, more preferably 30 minutes to 3 hours.

The precursor (A) to be fired may remain in the state obtained in the step (X), but from the viewpoint of efficiently causing the firing reaction to lower the firing temperature or shortening the firing time. It may be fired after being compacted. However, in this case, it is necessary to grind the obtained belite.

The belite obtained through the step (Y) is contained in a general Portland cement clinker obtained by firing at 1400 ° C. or higher even though the firing temperature is as low as 800 ° C. or lower. It contains α-C ₂ S (hexagonal system) and β-C ₂ S (monoclinic system). _{The α-C 2} S content in the entire mineral composition obtained by the XRD-Rietveld method of Belite is 10 to 20% by mass, and the β-C ₂ S content is 20 to 50% by mass. be.

The BET specific surface area of belite obtained through the step (Y) by the nitrogen adsorption method is 2.5 to 8 m ² / g.

The belite obtained by the production method of the present invention may be used alone as a hydraulic composition, or may be used as a material for a mixed hydraulic composition such as a mixed material of Portland cement.

For example, by mixing belite obtained in the present invention with ordinary Portland cement at a mass ratio (Belite / ordinary Portland cement) = 1/1, a hydraulic composition having a quality equivalent to that of low heat Portland cement is produced. It is possible. In this way, a plurality of types of Portland cement equivalent products can be produced from one type of Portland cement clinker.

Hereinafter, the present invention will be specifically described based on examples. Unless otherwise specified in the table, the content of each component indicates mass%.

[Example 1]
46.01 g of sodium orthosilicate (manufactured by Nacalai Tesque) and 500 g of water were mixed to obtain a 0.5 mol / L sodium silicate aqueous solution (pH 12). Separately, 118.075 g of calcium nitrate (manufactured by Kanto Chemical Co., Inc.) and 500 g of water were mixed to obtain a 1.0 mol / L calcium nitrate aqueous solution (pH 6).
While continuing nitrogen purging and stirring to the obtained aqueous sodium silicate solution, the obtained aqueous solution of calcium nitrate was added dropwise at a dropping rate of 12.5 ml / min to obtain an aqueous solution a1 having a pH of 11.6, and then the aqueous solution a1. Was stirred for 24 hours in a constant temperature environment of 40 ° C.
Then, after the aqueous solution a1 was filter-pressed, the obtained dehydrated cake was washed with 2 parts by mass of water with respect to 1 part by mass of the dehydrated cake. Then, it was dehydrated again with a filter press to obtain precursor b1.

The obtained precursor b1 was calcined in an air atmosphere at 600 ° C. for 3 hours ^{to obtain belite (I) (BET specific surface area of 5.4 m 2} / g).

[Example 2]
The dehydrated cake obtained after the filter press of the aqueous solution a1 was obtained in the same manner as in Example 1 except that it was not washed and dehydrated, ^{to obtain Belite (II) (BET specific surface area 2.9 m 2} / g).

[Example 3]
Instead of the calcium nitrate aqueous solution (pH 6), a calcium nitrate aqueous solution (pH 12) obtained by mixing 118.075 g of calcium nitrate (manufactured by Kanto Chemical Co., Inc.), 0.2 g of caustic soda (manufactured by Kanto Chemical Co., Inc.), and 500 g of water was used. ^{In the same manner as in Example 1, belite (III) (BET specific surface area 6.9 m 2} / g) was obtained except that an aqueous solution a3 having a pH of 12.1 was obtained instead of the aqueous solution a1 having a pH of 10.

[Example 4]
The dehydrated cake obtained after the filter press of the aqueous solution a3 was obtained in the same manner as in Example 3 except that it was not washed and dehydrated, ^{to obtain Belite (IV) (BET specific surface area 2.9 m 2} / g).

[Comparative Example 1]
Fine limestone powder and fine silica stone powder are mixed so that the Ca / Si molar ratio of the mixture is 2.0, and after calcining at 1000 ° C. for 1 hour, the obtained calcined product is pressure-molded into pellets. Was fired at 1450 ° C. for 1 hour. The obtained calcined product was crushed with a ball mill to obtain a brain specific surface area of 3000 cm ² / g, and then the pellet was pressure-molded again and calcined at 1450 ° C. for 1 hour to reduce the amount of free lime (f-CaO) to 0. A 1% by mass belite mass was obtained.
The obtained belite mass was crushed by a ball mill to obtain belite (V) (BET specific surface area 0.9 m ² / g).

≪Evaluation of precursor ignition loss≫
For each precursor obtained in the examples, the loss on ignition was evaluated when the dried product was dried to a constant weight at 110 ° C. The evaluation of ignition loss was based on the method specified in JIS R 5202 "Chemical analysis method of cement". That is, the weight loss when the sample was ignited to a constant temperature of 950 ° C. in the air atmosphere was measured.
The results are shown in Table 1.

≪Evaluation of the constituent phases of Beelite≫
The constituent phases of the belites obtained in Examples and Comparative Examples were quantitatively analyzed using the XRD-Rietveld method (TOPAS manufactured by BrukerAXS).
The results are shown in Table 1.

≪Evaluation of strength expression≫
For examples and belite obtained in Comparative Example, ordinary Portland cement: belite = 1: 1 was mixed with (mass ratio), further SO ₃ content in the sample after mixing with 2.0 wt% A mixed hydraulic composition was trial-produced by adding Nimizu gypsum (manufactured by Wako Pure Chemical Industries, Ltd., special grade reagent). Next, using the obtained mixed hydraulic composition, the mortar compressive strength (N / mm ² ) of the mortar specimen obtained by the following method was measured, and the strength expression of belite was evaluated.
The obtained mixed hydraulic composition corresponds to low-heat Portland cement, judging from the mineral composition.
Further, as a reference example, commercially available low-heat Portland cement (manufactured by Taiheiyo Cement Co., Ltd.) was used, and the compressive strength of mortar was evaluated in the same manner.
The results are shown in Table 1.

<< Preparation of mortar specimen >>
1) Using commercially available ordinary Portland cement (manufactured by Pacific Cement Co., Ltd.) whose chemical composition is shown in Table 2, ordinary Portland cement: belite = 1: 1 (mass ratio), and SO of the mixed hydraulic composition after mixing. ₃ A mixture of belite, ordinary Portland cement and dihydrate gypsum, which is blended with dihydrate gypsum so as to have a content of 2.0% by mass, is mixed in a pot mill for 15 minutes to produce a mixed hydraulic composition. did.

2) 45 g of the obtained mixed hydraulic composition, standard sand (JIS R 5201 "Physical test method for cement" Annex 2) 135 g, and 22.5 g of water are kneaded with a kneading spoon for 60 seconds, and then a solder paste mixer. (Manufactured by Shinky Co., Ltd., rotation speed 300 rpm) was kneaded for 30 seconds, and then kneaded again with a kneading spoon for 15 seconds to obtain a mortar.

3) The obtained mortar was packed in a 2 × 2 × 3 cm mold in one layer, vibrated with a table vibrator for 30 seconds, and then the upper surface of the specimen was smoothed using a metal straight edge. Then, the surface of the specimen was covered with a glass plate and cured in a moisture box (20 ± 1 ° C., relative humidity 90% or more) to obtain a mortar specimen.

According to the results in Table 1, the belite obtained in the examples is excellent in strength development even though it is obtained by firing at a lower temperature than the belite obtained in the comparative example. I understand.

Claims (5)

Next steps (X) and (Y):
(X) Calcium sulfate aqueous solution, calcium nitrate aqueous solution or calcium acetate aqueous solution is added to and stirred in the silicate compound aqueous solution to obtain an aqueous solution a having a pH of 9 to 14, and then nitrogen is purged while continuing to stir the aqueous solution a. , (Y) A method for producing belite, comprising a step of obtaining a precursor (A) and a step of firing the obtained precursor (A) at a temperature of 800 ° C. or lower to obtain belite. The method for producing belite according to claim 1, wherein the aqueous solution a is continuously stirred in the step (X) and heated to 30 to 90 ° C. The method for producing belite according to claim 1 or 2 , wherein the Ca / Si molar ratio in the precursor (A) is 1.9 to 2.1. The method for producing belite according to any one of claims 1 to 3, wherein the ignition loss (constant amount at 950 ° C.) of the precursor (A) is 11% by mass or less. The method for producing belite according to any one of claims 1 to 4 , wherein the aqueous solution of the silicic acid compound used in the step (X) contains sodium orthosilicate.